Studies are proposed to investigate the carcinogenicity of chronic oral administration of asbestos (chrysotile and amosite) to mice and rats during pregnancy, and F1 progeny for life; animals are dosed at two different concentrations of each fiber type. Animals, dying during the course of the experiment or sacrificed of the end of the experiment (2 years), will be autopsied and lesions, particularly in the G.I. tract, will be subjected to detailed histopathological examination.